But Kate reportedly had her heart set on the legendary singer because she represents 'true elegance, class and sophistication'.

'Dame Shirley was always top of her wish list for the wedding entertainment, and she's over the moon that she's agreed to perform for her,' a source told British newspaper The Sunday Mirror.

'Kate wanted high-end glamour and good old 'fashioned entertainment, and Dame Shirley was the perfect choice. She agreed to play the gig immediately and Kate can't wait for the big day. It will be a real highlight.'

According to the source, the 74-year-old soul-diva will receive 100,000 for her performance, but her decision to sing at Kate's wedding was never down to money.

The British fashion icon and the singer have been friends for years and have been pictured together on numerous occasions.

'She's got all the money she could ever need. She wanted to do it for Kate,' the source added. 'They have a real connection. Kate thinks she stands for true elegance, class and sophistication. As far as Kate's concerned she's only going to get married once so it has to be the day of her dreams. That's what she wants at her wedding.'